U.S. patent application number 09/791860 was filed with the patent office on 2002-05-02 for toner for electrostatic image development and method of producing the same.
This patent application is currently assigned to DAINIPPON INK AND CHEMICALS, INC.. Invention is credited to Hashizume, Toyomi, Hirabayashi, Kenichi, Ito, Takashi, Takayanagi, Hitoshi.
Application Number | 20020051923 09/791860 |
Document ID | / |
Family ID | 18754634 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020051923 |
Kind Code |
A1 |
Takayanagi, Hitoshi ; et
al. |
May 2, 2002 |
Toner for electrostatic image development and method of producing
the same
Abstract
The present invention provides a toner for electrostatic image
development made of a polyester resin having a spherical or
generally spherical shape, which allows the use of a so-called
oilless fixation system capable of fixing, without employing an
anti-offset solution as a heat roller fixation system, and which
also provides a developed image having excellent quality, and a
method of producing the same. The toner for electrostatic image
development comprises at least a binder resin and a colorant. The
binder resin is made of a polyester resin. The flow beginning
temperature Tfb of the toner, as measured by a constant load
extrusion type capillary rheometer, is 90.degree. C. or higher and
120.degree. C. or lower, the T1/2 temperature exceeds 120.degree.
C. and is 160.degree. C. or lower, and the flow ending temperature
Tend is 130.degree. C. or higher and 170.degree. C. or lower. Also
the toner has a spherical or generally spherical shape having an
average roundness (the average value of roundness is defined by
(the perimeter of a circle having the same area as that of a
projected area of the particles)/(the perimeter of a projected
image of particles)) of 0.97 or more. The toner having these
properties can be preferably produced by phase inversion at a low
shear within a range of 0.2-5 m/second employing an added alcohol
solvent.
Inventors: |
Takayanagi, Hitoshi;
(Omiya-shi, JP) ; Ito, Takashi; (Tokyo, JP)
; Hirabayashi, Kenichi; (Kitaadachi-gun, JP) ;
Hashizume, Toyomi; (Ichihara-shi, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN & HATTORI, LLP
1725 K STREET, NW.
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
DAINIPPON INK AND CHEMICALS,
INC.
Tokyo
JP
|
Family ID: |
18754634 |
Appl. No.: |
09/791860 |
Filed: |
February 26, 2001 |
Current U.S.
Class: |
430/108.4 ;
430/109.4; 430/111.4; 430/137.14; 430/137.19 |
Current CPC
Class: |
G03G 9/08793 20130101;
G03G 9/08795 20130101; G03G 9/0827 20130101; G03G 9/0819 20130101;
G03G 9/08755 20130101; G03G 9/08797 20130101 |
Class at
Publication: |
430/108.4 ;
430/109.4; 430/111.4; 430/137.14; 430/137.19 |
International
Class: |
G03G 009/087 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2000 |
JP |
2000-267767 |
Claims
What is claimed is:
1. A toner for electrostatic image development, comprising at least
a binder resin and a colorant, said binder resin being made of a
polyester resin, wherein the flow beginning temperature Tfb of the
toner, as measured by a constant load extrusion type capillary
rheometer, is 90.degree. C. or higher and 120.degree. C. or lower,
the T1/2 temperature exceeds 120.degree. C. and is 160.degree. C.
or lower, and the flow ending temperature Tend is 130.degree. C. or
higher and 170.degree. C. or lower, and wherein said toner has a
spherical or generally spherical shape having an average roundness
(the average value of roundness is defined by (the perimeter of a
circle having the same area as that of a projected area of the
particles)/(the perimeter of a projected image of the particles))
of 0.97 or more.
2. A toner for electrostatic image development in accordance with
claim 1, wherein said binder resin contains a crosslinked polyester
resin and the content of a tetrahydrofuran-insoluble fraction of
said binder resin in the toner is within a range of 0.2-20% by
weight.
3. A toner for electrostatic image development in accordance with
claim 2, further comprising a straight-chain polyester resin.
4. A toner for electrostatic image development in accordance with
claim 1, wherein said binder resin is a mixture of: (A) a
straight-chain polyester resin in which the T1/2 temperature, as
measured by the constant load extrusion type capillary rheometer,
is 80.degree. C. or higher and 120.degree. C. or lower, and the
glass transition temperature Tg is 40.degree. C. or higher and
75.degree. C. or lower, and (B) a crosslinked polyester resin in
which the T1/2 temperature, as measured by the constant load
extrusion type capillary rheometer, exceeds 120.degree. C. and is
210.degree. C. or lower, and the glass transition temperature Tg is
40.degree. C. or higher and 75.degree. C. or lower, and wherein a
weight ratio of said resin (A) to said resin (B), (A)/(B), is
within a range of 20/80-80/20, and wherein said toner satisfies the
relationship: 20.degree.
C..ltoreq.T1/2(B)-T1/2(A).ltoreq.120.degree. C. where T1/2(A) and
T1/2(B) respectively represent the T1/2 temperature of said resin
(A) and said resin (B).
5. A toner for electrostatic image development in accordance with
claim 1, which satisfies the relationship: T1/2 (toner).gtoreq.T1/2
(resin) where T1/2 (toner) and T1/2 (resin) respectively represent
the T1/2 temperatures as measured by the constant load extrusion
type capillary rheometer of said toner and said polyester resin
used as said binder resin.
6. A toner for electrostatic image development in accordance with
claim 1, wherein the weight-average molecular weight, as measured
by gel permeation chromatography of a tetrahydrofuran-soluble
fraction of said binder resin in said toner, is 30,000 or more, the
(weight-average molecular weight)/(number-average molecular weight)
is 12 or more, the area ratio of a molecular weight of 600,000 or
more is 0.5% or more, and the area ratio of a molecular weight of
10,000 or less is within a range of 20-80%.
7. A toner for electrostatic image development in accordance with
claim 1, wherein said binder resin has a carboxyl group, and the
acid value of said binder resin is within a range of 1-30
KOHmg/g.
8. A toner for electrostatic image development in accordance with
claim 7, wherein a portion of the carboxyl group in said binder
resin is converted into carboxylate salts neutralized with a
base.
9. A toner for electrostatic image development in accordance with
claim 1, further comprising a releasing agent.
10. A toner for electrostatic image development in accordance with
claim 9, wherein said releasing agent comprises a synthetic ester
and/or a natural ester wax.
11. A toner for electrostatic image development in accordance with
claim 1, further comprising a positive charge control agent.
12. An image forming method, which comprises employing the toner of
claim 1.
13. An image forming method in accordance with claim 12, wherein an
anti-offset solution is not employed on a fixing heat roller.
14. A method of producing the toner for electrostatic image
development of claim 1, which comprises a step of mixing a mixture
of a polyester resin having a carboxyl group, a colorant, and a
releasing agent with an aqueous medium in the presence of a base
and emulsifying the admixture (emulsifying step) to prepare a
suspension of colored particles (I); and a step of separating said
colored particles (I) from said aqueous medium and drying said
colored particles; wherein said polyester resin having a carboxyl
group is a mixture of: (A) a straight-chain polyester resin in
which the T1/2 temperature, as measured by the constant load
extrusion type capillary rheometer, is 80.degree. C. or higher and
120.degree. C. or lower, and the glass transition temperature Tg is
40.degree. C. or higher and 75.degree. C. or lower, and (B) a
crosslinked polyester resin in which the T1/2 temperature, as
measured by the constant load extrusion type capillary rheometer,
exceeds 120.degree. C. and is 210.degree. C. or lower, and the
glass transition temperature Tg is 40.degree. C. or higher and
75.degree. C. or lower, and wherein a weight ratio of said resin
(A) to said resin (B), (A)/(B), is within a range of 20/80-80/20,
and wherein said toner satisfies the relationship: 20.degree.
C..ltoreq.T1/2(B)-T1/2(- A).ltoreq.120.degree. C. where T1/2(A) and
T1/2(B) respectively represent the T1/2 temperature of said resin
(A) and said resin (B).
15. A method of producing the toner for electrostatic image
development in accordance with claim 14, wherein the polyester
resin having a carboxyl group, the colorant, and the releasing
agent in said mixture are previously dissolved or dispersed in an
organic solvent, and said colored particles (I) are produced by
further adding a phase inversion accelerator in said emulsifying
step.
16. A method of producing the toner for electrostatic image
development in accordance with claim 15, wherein said phase
inversion accelerator is an alcohol solvent.
17. A method of producing the toner for electrostatic image
development in accordance with claim 15, wherein stirring in said
emulsifying step is performed by a stirring blade at a peripheral
speed within a range of 0.2-5 m/second.
18. A method of producing the toner for electrostatic image
development in accordance with claim 17, wherein said stirring
blade is a max blend blade or a full-zone blade.
19. A method of producing the toner for electrostatic image
development in accordance with claim 14, wherein the acid value of
said polyester resin having a carboxyl group is within a range of
1-30 KOHmg/g.
20. A method of producing the toner for electrostatic image
development in accordance with claim 14, wherein said releasing
agent comprises a synthetic ester and/or a natural ester wax.
21. A method of producing the toner for electrostatic image
development in accordance with claim 14, further comprising a
positive charge control agent.
22. A method of producing the toner for electrostatic image
development in accordance with claim 14, which comprises adding a
suspension of microparticles (II), obtained by emulsifying a
mixture of a resin capable of being provided with self-water
dispersibility and/or water solubility by a positive charge control
agent and neutralization with an aqueous medium in the presence of
a neutralizer, to a suspension of said colored particles (I);
adding a compound having the reverse polarity as compared with said
neutralizer to form microparticles (III) in which microparticles
(II) are deposited on the surface of said colored particles (I);
separating said microparticles (III) from said aqueous medium; and
drying said microparticles (III).
23. A method of producing the toner for electrostatic image
development in accordance with claim 14, wherein the colorant and
releasing agent used in the emulsifying step during the preparation
of the suspension of said colored particles (I) are previously
kneaded and dispersed by a wet process.
Description
BACKGROUND OF THE INVENTION
[0001] 1. FIELD OF THE INVENTION
[0002] The present invention relates to a toner for electrostatic
image development which is preferably employed in
electrophotographic copying machines, printers, and facsimiles, and
is also employed in toner-jet type printers.
[0003] 2. DESCRIPTION OF THE RELATED ART
[0004] In electrophotographic copying machines, printers, and
facsimiles, the following needs for the toner have recently been
enhanced for cost reduction and size reduction of the machines as
well as power saving and resource saving, including a further
improvement in the quality of the printed image. The needs
include:
[0005] (1) improvement in the definition and gradation of the
printed image, reduction in the thickness of the toner layer,
reduction in the amount of wasted toner, reduction in the particle
diameter and spheroidizing of the toner for reducing the amount of
the toner consumed per page,
[0006] (2) decrease in the fixation temperature for reduction in
power consumed,
[0007] (3) oilless fixation for simplification of the machines;
[0008] (4) improvement in the hue, transparency and gloss in
full-color images,
[0009] (5) reduction in VOCs (volatile organic compounds) during
fixation which are likely to exert an adverse effect on human
health and the like.
[0010] A reduction in the particle diameter of the powdered toner
prepared by a pulverization method, which has been employed for a
long time, can be basically carried out. However, with the
reduction in particle size, the following problems arise: (1) it
becomes difficult to control the charge because of an increase in
the amount of colorants and waxes exposed on the surface of the
toner particles, (2) the fluidity of the powder is lowered by the
unfixed shape of the toner particles, and (3) the energy cost
required for production increases, thus, in actuality, it is
difficult to sufficiently satisfy the needs described above using a
toner having an unfixed shape prepared by employing the
pulverization method.
[0011] Therefore, development of a spherical toner having a small
particle diameter has been intensively carried out by the
polymerization method or the emulsification/dispersion method.
Although various methods are known for producing a toner employing
the polymerization method, the suspension polymerization method has
been widely employed which comprises: uniformly dissolving and
dispersing a monomer, a polymerization initiator, a colorant, and a
charge control agent; adding the mixture to an aqueous medium
containing a dispersion stabilizer while stirring to form oil
droplets; and heating, thereby causing the polymerization reaction
to produce toner particles. Although the reduction in particle
diameter and spheroidizing can be satisfactorily conducted by the
polymerization method, a principal component of the binder resin is
limited to a radically-polymerizable vinyl polymer, S and toner
particles made of a polyester resin or epoxy resin suited for use
as a color toner cannot be produced by the polymerization method.
It is difficult to reduce VOCs (volatile organic compounds made of
an unreacted monomer) by the polymerization method, and
improvements are required.
[0012] As is disclosed in Japanese Unexamined Patent Application,
First Publication No. Hei 5-66600 and Japanese Unexamined Patent
Application, First Publication No. Hei 8-211655, the method of
producing a toner employing the emulsification/dispersion method
comprises mixing a mixture of a binder resin and a colorant with an
aqueous medium and emulsifying them to obtain toner particles, and
has the following advantages: (1) possible binder resins can be
widely selected, (2) the reduction of VOCs is easy to realize, and
(3) the concentration of the colorant is easy to change optionally
within a range of low to high values, as compared with the
polymerization method, in addition to the advantage that it is easy
to cope with the reduction in particle diameter and spheroidizing
of the toner similar to the polymerization method.
[0013] It is generally known that a polyester resin is more
preferable than a styrene-acrylic resin as a binder resin for
toner, which can reduce the fixing temperature and forms a smooth
image surface by melting rapidly during fixation, and a polyester
resin having excellent pliability is particularly preferably
employed in the color toner.
[0014] As described above, toner particles containing a polyester
resin as the principal component cannot be produced by the
polymerization method as described above. Therefore, a spherical or
generally spherical toner having a small particle diameter
containing a polyester resin as the binder resin obtained by the
emulsification/dispersion method has attracted special interest
recently.
[0015] However, in the spherical toner obtained by the
emulsification/dispersion method, reduction of the fixation
temperature and widening of the anti-offset temperature range are
not necessarily sufficiently realized. Therefore, a fixing drum is
coated with silicone oil to prevent the toner from adhering to the
fixing drum during fixation. An improvement in the thermal
properties of the spherical toner makes it possible to obtain an
oilless toner having high anti-offset properties while utilizing
its high image quality.
[0016] Techniques are disclosed in Japanese Unexamined Patent
Application, First Publication Nos. Hei 9-311502, Hei 5-66600, Hei
8-211655, Hei 6-332224, Hei 6-332225, and Hei 10-319639 as methods
for producing a toner containing a polyester resin as a binder
resin, for example. However, not all of the problems to be solved
by the present invention can be solved using these methods.
[0017] Japanese Unexamined Patent Application, First Publication
No. Hei 5-66600 discloses a method of providing a mixture of a
binder resin, a colorant, and an organic solvent having self-water
dispersibility and/or water solubility by neutralizing the binder
resin, thereby dispersing the mixture in an aqueous medium.
However, this technique is intended exclusively for a
styrene-acrylic resin as the binder resin and is not necessarily
suited for fixation at low temperatures and a color toner.
Furthermore, the publication does not make any reference to the
composition of the binder resin in the toner employing a polyester
resin which makes fixation at low temperatures and oilless fixation
possible.
[0018] Japanese Unexamined Patent Application, First Publication
Nos. Hei 6-332224 and Hei 6-332225 each disclose a method of
dispersing a mixture of a polyester resin, a colorant, an organic
solvent and a specific dispersion stabilizer in an aqueous medium.
According to this technique, the polyester resin is dispersed in
the aqueous medium by only an action of the dispersion stabilizer
because the polyester resin itself has no self-water
dispersibility. According to the system of dispersing employing the
dispersion stabilizer, dispersion is hardly performed at low shear,
and, therefore, dispersion must be performed at high shear
employing a homomixer or the like. As a result, coarse particles
and microparticles tend to occur, resulting in large classification
loss. This publication does not make any reference to a composition
which can provide the fixation at low temperatures and oilless
fixation. A toner containing a high-molecular weight component or a
tetrahydrofuran-insolub- le fraction has a wide particle size
distribution, and, therefore, there is a limit in
manufacturing.
[0019] Japanese Unexamined Patent Application, First Publication
No. Hei 9-311502 discloses a method of mechanically dispersing a
mixture of a polyester resin and a colorant in an aqueous medium by
reducing the viscosity due to melting with heating without
employing a solvent. According to this method, there is a limit in
molecular weight of a usable resin and those containing a large
amount of a high-molecular weight component result in the breakage
of the molecular chain, thus making it impossible to raise the hot
offset temperature. As a result, it is impossible to attain a good
fixing range in the oilless fixation system, which is the problem
to be solved by the present invention.
[0020] Japanese Unexamined Patent Application, First Publication
No. Hei 8-211655 discloses a method of providing a mixture of a
polyester resin, a colorant, and an organic solvent having
self-water dispersibility and/or water solubility by
neutralization, thereby dispersing the mixture in an aqueous
medium. This technique can be employed in a color toner and allows
the provision of a spherical toner having a small particle diameter
so that a part of the problem to be solved by the present invention
can be solved. However, this publication does not make any
reference to a composition which can attain fixation at low
temperatures and a good fixation range in the oilless fixation
system.
[0021] A polyester resin toner obtained by the
emulsification/dispersion method which has hitherto been employed
mainly contains a straight-chain resin having a comparatively low
molecular weight as the binder resin. Therefore, it is essential to
coat a fixing heat roller with an anti-offset solution such as
silicone oil. Thus, the fixation in this method cannot be oilless
fixation. Moreover, even if oilless fixation is employed in the
above method, there are problems in that due to transfer of the
silicone oil to a printing paper or an OHP sheet, it is difficult
to write on the paper or sheet after printing, or the paper or
sheet becomes greasy with the oil, in addition to the problem of
maintenance. There is also a problem in that the peel strength is
not necessarily sufficient since it varies depending on the
purposes. There is also a problem such as large emulsification loss
and classification loss due to a poor particle size
distribution.
BRIEF SUMMARY OF THE INVENTION
[0022] The present invention has been made in light of the
circumstances described above, and an object of the present
invention is to provide a toner for electrostatic image development
made of a polyester resin having a spherical or generally spherical
shape, which allows the use of a so-called oilless fixation system
capable of fixing in a good fixing range, without employing an
anti-offset solution, as a heat roller fixation system, and which
also provides a developed image having excellent quality, and a
method of producing the same.
[0023] Another object of the present invention is to provide an
image forming method employing the toner for electrostatic image
development, which solves the problems described above.
[0024] Still another object of the present invention is to provide
a method of producing the toner for electrostatic image development
which solves the problems described above.
[0025] The present inventors have directed their attention to the
flow tester values of the toner, namely, the flow beginning
temperature Tfb as measured by a constant load extrusion type
capillary rheometer, the T1/2 temperature, and the flow ending
temperature Tend. Thus, as a result of diligent research, the
present inventors have found that a good fixation initiation
temperature and anti-hot offset properties are obtained in the
oilless fixation system by controlling the above-mentioned
temperatures within a specific range, thus completing the present
invention.
[0026] That is, the present invention provides a toner for
electrostatic image development, comprising at least a binder resin
and a colorant, said binder resin being made of a polyester resin,
wherein the flow beginning temperature Tfb of the toner, as
measured by a constant load extrusion type capillary rheometer, is
90.degree. C. or higher and 120.degree. C. or lower, the T1/2
temperature exceeds 120.degree. C. and is 160.degree. C. or lower,
and the flow ending temperature Tend is 130.degree. C. or higher
and 170.degree. C. or lower, and wherein said toner has a spherical
or generally spherical shape having an average roundness (the
average value of roundness is defined by (the perimeter of a circle
having the same area as that of a projected area of the
particles)/(the perimeter of a projected image of the particles))
of 0.97 or more.
[0027] Since the flow tester values of a spherical or generally
spherical toner containing a polyester resin as a binder resin are
controlled within a specific range, the toner for electrostatic
image development of the present invention has a good fixation
initiation temperature and anti-hot offset temperature for use with
an oilless fixation heat roller. The toner for electrostatic image
development of the present invention is superior in the fluidity of
the powder, transfer efficiency, definition, and gradation as a
result of spheroidizing and reduction in the particle diameter,
thus making it possible to provide a developed image having
excellent quality.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0028] FIGS. 1A and 1B are schematic drawings for explaining how to
determine flow tester values, in which FIG. 1A is a side sectional
view showing an outline of a measuring device and FIG. 1B is a
graph for explaining a method of determining each of the flow
tester values from the measured values.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention will now be described in detail.
[0030] The toner for electrostatic image development of the present
invention comprises at least a binder resin and a colorant, the
binder resin being made of a polyester resin. The polyester resin
employed is synthesized by dehydration condensation of a polybasic
acid and a polyhydric alcohol.
[0031] Examples of the polybasic acid include: aromatic carboxylic
acids such as terephthalic acid, isophthalic acid, phthalic
anhydride, trimellitic anhydride, pyromellitic acid, and
naphthalenedicarboxylic acid; aliphatic carboxylic acids such as
maleic anhydride, fumaric acid, succinic acid, alkenylsuccinic
anhydride, and adipic acid; and alicyclic carboxylic acids such as
cyclohexanedicarboxylic acid. These polybasic acids can be used
alone or in combination. Among these polybasic acids, an aromatic
carboxylic acid is preferably employed.
[0032] Examples of the polyhydric alcohol include aliphatic diols
such as ethylene glycol, diethylene glycol, triethylene glycol,
propylene glycol, butanediol, hexanediol, neopentyl glycol, and
glycerin; alicyclic diols such as cyclohexanediol,
cyclohexanedimethanol, and hydrogenated bisphenol A; and aromatic
diols such as an ethylene oxide adduct of bisphenol A and a
propylene oxide adduct of bisphenol A. These polyhydric alcohols
can be used alone or in combination. Among these polyhydric
alcohols, aromatic diols and alicyclic diols are preferred, and
aromatic diols are more preferred.
[0033] A hydroxyl group at a polymer terminal and/or a carboxyl
group may be esterified by further adding monocarboxylic acid
and/or monoalcohol to the polyester resin obtained by the
polycondensation of the polyhydric carboxylic acid and polyhydric
alcohol, thereby controlling the acid value of the polyester
resin.
[0034] Examples of the monocarboxylic acid employed for this
purpose include acetic acid, acetic anhydride, benzoic acid,
trichloroacetic acid, trifluoroacetic acid, propionic anhydride,
and the like. Examples of the monoalcohol include methanol,
ethanol, propanol, octanol, 2-ethylhexanol, trifluoroethanol,
trichloroethanol, hexafluoroisopropanol, phenol, and the like.
[0035] The polyester resin can be produced by the condensation
reaction of the polyhydric alcohol and polyhydric carboxylic acid
according to a conventional method. For example, it can be produced
by charging the polyhydric alcohol and polyhydric carboxylic acid
in a reaction vessel equipped with a thermometer, a stirrer, and a
dropping condenser; heating them to 150-250.degree. C. in the
presence of an inert gas (e.g. nitrogen gas); continuously removing
a low-molecular weight compound out of the reaction system;
terminating the reaction at a point of time when the acid value
reaches a predetermined value; and cooling to obtain a desired
reaction product.
[0036] In the synthesis of the polyester resin, a catalyst may be
employed. Examples of the catalyst include esterification
catalysts, for example, an organometallic compound (e.g. dibutyltin
dilaurate and dibutyltin oxide, etc.) and metal alkoxide (e.g.
tetrabutyl titanate, etc.). For the case where the carboxylic acid
component is a lower alkyl ester, ester interexchange catalysts can
be used, for example, a metal acetate (e.g. zinc acetate, lead
acetate, magnesium acetate, etc.), a metal oxide (e.g. zinc oxide,
antimony oxide, etc.) and a metal alkoxide (e.g. tetrabutyl
titanate, etc.). The amount of the catalyst is preferably within a
range of 0.01-1% by weight based on the total amount of the raw
materials.
[0037] To produce a crosslinked polyester resin in such a
polycondensation reaction, a polybasic acid having three or more
carboxyl groups per molecule or an anhydride thereof and/or a
polyhydric alcohol having three or more hydroxyl groups per
molecule are preferably employed as essential synthetic raw
materials.
[0038] Flow tester values of the toner for electrostatic image
development of the present invention comprising the binder resin
thus obtained as the binder resin are within the following range.
With respect to the flow tester values of the toner for
electrostatic image development, the flow beginning temperature
Tfb, as measured by a constant load extrusion type capillary
rheometer, is 90.degree. C. or higher and 120.degree. C. or lower,
the T1/2 temperature exceeds 120.degree. C. and is 160.degree. C.
or lower, and the flow ending temperature Tend is 130.degree. C. or
higher and 170.degree. C. or lower. The toner for electrostatic
image development of the present invention has good fixation
properties using these flow tester values.
[0039] The flow beginning temperature Tfb as measured by the
constant load extrusion type capillary rheometer, the T1/2
temperature, and the flow ending temperature Tend are determined by
employing a FLOW TESTER "CFT-500" produced by Shimadzu Corporation.
Employing a flow tester as shown in FIG. 1A, a cylinder 2 equipped
with a nozzle 1 having a nozzle diameter D of 1.0 mm .PHI. and a
nozzle length (depth) L of 1.0 mm is filled with a toner 3 (weight:
1.5 g) and a load per unit area (cm.sup.2) of 30 kg is applied from
the side opposite the nozzle 1 and, furthermore, the cylinder is
heated at a heating speed of 6.degree. C. per minute. Then, a
stroke S (depression value of a loaded surface 4) of the loaded
surface is measured. That is, the relationship between the
increased temperature and the stroke S is determined as shown in
FIG. 1B and the temperature at which the stroke 3 increases rapidly
after the beginning of flowing of the toner 3 through the nozzle 1,
where the curve rises, is taken as Tfb, while the temperature at
which flowing of the toner 3 through the nozzle 1 is nearly
completed, where the curve flattens, is taken as Tend. The
temperature at S1/2, which is an intermediate value between the
stroke Sfb at Tfb and the stroke Send at Tend, is taken as the T1/2
temperature.
[0040] With respect to the measurement by the heating method
employing this device, the process in which the state of the sample
changes from a solid region to a flow region by way of a transition
region and a rubber-like elasticity region can be continuously
measured by testing while increasing the temperature at a fixed
rate with respect to a lapse of time during the test. The shear
speed and viscosity at each temperature in the flowing region can
be simply measured by employing this device.
[0041] The flow beginning temperature Tfb is an index for sharp
melting properties and fixation properties at low temperatures of
the toner. When the flow beginning temperature is too high, the
fixation properties at low temperatures become inferior and a cold
offset is liable to occur. On the other hand, when the flow
beginning temperature is too low, the storage stability is lowered
and a hot offset is liable to occur.
[0042] Accordingly, the flow beginning temperature Tfb of the toner
for electrostatic image development is preferably 90.degree. C. or
higher and 115.degree. C. or lower, and more preferably within a
range of 90-110.degree. C.
[0043] The melting point T1/2 measured by the "1/2 method" and the
flow ending temperature Tend are indexes for anti-hot offset
properties. When any of the melting point T1/2 measured by the "1/2
method" and the flow ending temperature Tend is too high, the
particle size distribution becomes inferior during the formation of
particles because the viscosity of the solution increases. On the
other hand, when any of the melting point T1/2 measured by the "1/2
method" and the flow ending temperature Tend is too low, an offset
is liable to occur, thereby lowering the practicability. Therefore,
the melting point T1/2 measured by the "1/2 method" preferably
exceeds 120.degree. C. and is 155.degree. C. or lower, and more
preferably is within a range of 130-150.degree. C., while the flow
ending temperature Tend is preferably 130.degree. C. or higher and
165.degree. C. or lower, and more preferably 140.degree. C. or
higher and 160.degree. C. or lower. It becomes possible to
accomplish fixation within a wide temperature range by setting Tfb,
T1/2, and Tend within the ranges described above.
[0044] The toner for electrostatic image development of the present
invention has a spherical or generally spherical shape having an
average roundness (the average value of roundness is defined by
(the perimeter of a circle having the same area as that of a
projected area of the particles)/(the perimeter of a projected
image of the particles)) of 0.97 or more, and preferably 0.98 or
more.
[0045] Since the toner for electrostatic image development of the
present invention has such a spherical or generally spherical
shape, it is possible to guarantee good powder fluidity even after
a reduction in the particle diameter and to guarantee good transfer
efficiency, thus making it possible to form an image having
excellent quality (e.g. definition, gradation, etc.). When the
average roundness is smaller than 0.97, that is, when the shape
changes from the spherical shape toward an irregular shape, the
transfer efficiency is lowered, which is not preferred. The average
roundness can also be determined by taking an SEM (scanning
electron microscope) photograph of the toner particles, followed by
measurements and calculations, but is more easily obtained by
employing a flow type particle image analyzer FPIP-1000 produced by
Toa Iyo Denshi Co., Ltd. In the present invention, the average
roundness was measured by this apparatus.
[0046] In such a toner for electrostatic image development, the
binder resin contains a crosslinked polyester resin, and the
content of a tetrahydrofuran-insoluble fraction of the binder resin
in the toner is within a range of 0.2-20% by weight, preferably
within a range of 0.5-10% by weight, and more preferably within a
range of 0.5-6% by weight. When using, as the binder resin in the
toner, a polyester resin wherein the content of the
tetrahydrofuran-insoluble fraction is within a range of 0.2-20% by
weight, good anti-hot offset properties can be guaranteed, which is
preferred.
[0047] When the content is less than 0.2% by weight, the effect of
improving the anti-hot offset properties becomes poor, which is not
preferred. On the other hand, when the content is greater than 20%
by weight, the viscosity of the solution becomes too high, and the
particle size distribution becomes inferior during the formation of
the particles. Furthermore, the fixation beginning temperature
increases and the balance of the fixation properties becomes poor,
which is not preferred.
[0048] The amount of the tetrahydrofuran-insoluble fraction is
determined in the following manner. That is, 1 g of the toner is
accurately weighed and completely dissolved in 40 ml of
tetrahydrofuran. After 2 g of Radioloite (#700 produced by Showa
Chemical Co., Ltd.) is uniformly disposed in a funnel (diameter: 40
mm) on which a Kiriyama filter paper (No. 3) is placed, the
solution is filtered and the cake is put in an aluminum petri dish.
After drying at 140.degree. C. for one hour, the dry weight is
measured. Then, a value (percentage) is calculated by dividing the
residual resin amount in the dry weight by the initial toner sample
amount and this value is taken as the insoluble fraction. Although
additives such as pigment, wax, external additives, and the like
are contained in the toner, the THF-insoluble fraction of the
binder resin is calculated considering their content and whether
they are soluble in THF.
[0049] The binder resin more preferably contains a straight-chain
polyester resin. In the toner for electrostatic image development,
the binder resin may be formed of a kind of a polyester resin, but
practically it is preferable to employ a resin prepared by blending
a crosslinked polyester resin having a high molecular weight and a
high viscosity with a straight-chain polyester resin having a low
molecular weight and a low viscosity in order to obtain a good
fixation beginning temperature and anti-hot offset properties in
view of the production of the resin. As used herein, the term
"crosslinked polyester resin" refers to a resin containing a
component which is insoluble in tetrahydrofuran, while the term
"straight-chain resin" refers to a resin which contains no
crosslinking agent component and is soluble in tetrahydrofuran.
[0050] In the present invention, when employing a mixture of the
straight-chain polyester resin and a crosslinked polyester resin as
the binder resin, the mixture is preferably a mixture of a
straight-chain polyester resin (A) and a crosslinked polyester
resin (B), satisfying the following conditions.
[0051] That is, the mixture is preferably a mixture of:
[0052] (A) a straight-chain polyester resin in which the T1/2
temperature, as measured by the constant load extrusion type
capillary rheometer, is 80.degree. C. or higher and 120.degree. C.
or lower and the glass transition temperature Tg is 40.degree. C.
or higher and 75.degree. C. or lower, and
[0053] (B) a crosslinked polyester resin in which the T1/2
temperature, as measured by the constant load extrusion type
capillary rheometer, exceeds 120.degree. C. and is 210.degree. C.
or lower and the glass transition temperature Tg is 40.degree. C.
or higher and 75.degree. C. or lower, and wherein
[0054] a weight ratio of resin (A) to resin (B), (A)/(B), is within
a range of 20/80-80/20, and wherein the mixture satisfies the
relationship:
20.degree. C..ltoreq.T1/2(B)-T1/2(A).ltoreq.120.degree. C.
[0055] where T1/2(A) and T1/2(B) respectively represent the T1/2
temperatures of resin (A) and resin (B).
[0056] Considering the properties at each temperature as measured
by the constant load extrusion type capillary rheometer, the
melting point T1/2(A) of resin (A) measured by the "1/2 method" is
an index for imparting sharp melting properties and fixation
properties at low temperatures, and T1/2(A) is preferably within a
range of 80-115.degree. C., and more preferably within a range of
90-110.degree. C.
[0057] Resin (A) defined by these properties has a low softening
temperature and sufficiently melts even for the case where the
thermal energy is reduced as a result of the reduction of the
temperature of a heat roller or the increasing of a processing
speed in the fixation process employing the heat roller, thus
exhibiting performances such as excellent cold offset and fixation
properties at low temperatures.
[0058] When both of the melting point T1/2(B) of resin (B) measured
by the "1/2 method" and the flow ending temperature Tend are too
low, a hot offset is liable to occur. On the other hand, when both
of them are too high, the particle size distribution becomes
inferior during the formation of the particles, thereby lowering
the productivity. Therefore, T1/2(B) is preferably within a range
of 125-210.degree. C., and more preferably within a range of
130-200.degree. C.
[0059] Since resin (B) defined by these properties has strong
rubber elasticity and a high melt viscosity, the internal cohesive
force of the molten toner layer is maintained even during melting
while heating in the fixation process and a hot offset rarely
occurs, and the resin exhibits excellent resistance to abrasion
after fixation because of its toughness.
[0060] By incorporating resin (A) and resin (B) with a good
balance, a toner capable of sufficiently providing the anti-offset
properties and fixation properties within a wide temperature range
can be provided.
[0061] When the weight ratio of resin (A) to resin (B), (A)/(B), is
too small, the fixation properties are affected. On the other hand,
when the weight ratio is too large, the anti-offset properties are
affected. Therefore, the weight ratio is preferably within a range
of 20/80-80/20, and more preferably within a range of
30/70-70/30.
[0062] When the melting temperature measured by the "1/2 method" of
resin (A) and that of resin (B) are T1/2(A) and T1/2(B),
respectively, the following expression T1/2(A) <T1/2(B) may be
established. T1/2(A)-1/2(B) is preferably within a range of
20-120.degree. C., and more preferably within a range of
30-110.degree. C., so as to uniformly mix during the melt-kneading
without causing a problem due to a difference in viscosity between
the resins in view of the trade-off between the fixation properties
at low temperatures and the anti-offset properties.
[0063] The T1/2 temperature, as measured by the constant load
extrusion type capillary rheometer, is a value obtained in the same
manner as described previously in FIG. 1A and FIG. 1B, except that
the measurement is performed with respect to the resin instead of
the toner. The glass transition temperature Tg is a value measured
at a heating speed of 10.degree. C. per minute by the second-run
method employing a Differential Scanning Calorimeter "DSC-50"
produced by Shimadzu Corporation in the present invention.
[0064] The glass transition temperature of the straight-chain
polyester resin (A) and crosslinked polyester resin (B) is
preferably 40.degree. C. or higher and 75.degree. C. or lower. When
the glass transition temperature Tg is less than 40.degree. C., the
resulting toner tends to cause blocking (a phenomenon wherein
particles of the toner agglomerate to form an agglomerate) during
storage or in a developing apparatus. On the other hand, when the
glass transition temperature exceeds 75.degree. C., the fixation
temperature of the toner increases, which is not preferable.
[0065] When employing, as the polyester resin which serves as the
binder resin, the straight-chain polyester resin (A) and
crosslinked polyester resin (B) which satisfy the relationship
described above, the resulting toner has good fixation properties,
which is preferred.
[0066] The toner of the present invention and the polyester resin
used as the binder resin preferably satisfy the following
relationship: T1/2 (toner).gtoreq.T1/2 (resin), where T1/2 (toner)
and T1/2 (resin) respectively represent the T1/2 temperatures of
the toner an the resin as measured by the constant load extrusion
type capillary rheometer. When employing a polyester resin which
satisfies the relationship, the resulting toner has better fixation
properties.
[0067] As described hereinafter, when the pigment, as a component
of the toner, is dispersed by the wet dispersion process of
dissolving and dispersing a polyester resin in a solvent and
kneading the mixture in a ball mill, molecular breakage of the
binder resin (polyester resin) does not occur, thus causing no
change in the molecular weight of the binder resin. Accordingly,
when employing a mixture obtained by the wet dispersion process,
which contains as components, a binder resin, a wax, and an organic
solvent, it is possible to satisfy the relationship: T1/2
(toner).gtoreq.T1/2 (resin).
[0068] On the other hand, properties of the binder resin are
changed by breakage of a polymer chain during the melt-kneading in
the toner obtained by the pulverization process so that the
relationship T1/2 (toner)<T1/2 (resin) is established.
Therefore, in order to obtain the oilless fixation properties as
well as good fixation properties at low temperatures and anti-hot
offset properties, it is preferable to satisfy the relationship
T1/2 (toner).gtoreq.T1/2 (resin), as described in the present
invention, in view of obtaining a good balance between the fixation
properties at low temperatures and the anti-hot offset properties,
as well as simplicity in the synthesis of the resin (it is not
necessary to synthesize a high-viscosity resin because no breakage
of the polymer chain occurs).
[0069] To obtain good fixation properties, the binder resin made of
the polyester resin preferably satisfy all of the following
conditions:
[0070] (1) the weight-average molecular weight is 30,000 or more,
and more preferably 37,000 or more;
[0071] (2) the (weight-average molecular weight Mw)/(number-average
molecular weight Mn) is 12 or more, and more preferably 15 or
more;
[0072] (3) the area ratio of a component having a molecular weight
of 600,000 is 0.5% or more, and more preferably 0.7% or more;
and
[0073] (4) the area ratio of a component having a molecular weight
of 10,000 or less is within a range of 20-80%, and more preferably
within a range of 30-70%, in the measurement of the molecular
weight by gel permeation chromatography (GPC) of the
tetrahydrofuran(THF)-soluble fraction.
[0074] In the toner according to the present invention, a
high-molecular weight component having a molecular weight of
600,000 or higher is effective in guaranteeing the anti-hot offset
properties. A toner in which a binder resin containing the
high-molecular weight component having a molecular weight of
600,000 or more can be suitably used with a fixing device of the
oilless fixation system. On the other hand, a low-molecular weight
component having a molecular weight of 10,000 or less is effective
in lowering the melt viscosity of the toner, thereby attaining
sharp melting properties and lowering the fixation initiation
temperature. To obtain good fixation properties such as fixation at
low temperatures and anti-hot offset properties, the binder resin
preferably has such broad molecular weight distribution. In the
granulation of the toner particles employing the
emulsification/dispersion method, use of a low-molecular weight
component is also preferable in view of reduction in viscosity of
the resin solution.
[0075] The molecular weight of the THF-soluble fraction in the
binder resin is determined in the following manner. That is, the
THF-soluble fraction is collected by filtering through a filter
(0.2 .mu.m) and measured in a THF solvent (flow rate: 0.6 ml/min,
temperature: 40.degree. C.) employing GPC.multidot.HLC-8120
produced by Tosoh Corporation and three columns "TSKgel Super HM-M"
(15 cm) produced by Tosoh Corporation, and then the molecular
weight calculated by employing a molecular weight calibration curve
made using a monodisperse polystyrene standard sample.
[0076] In the present invention, the molecular weight in the
specific range described above of the tetrahydrofuran-insoluble
fraction and tetrahydrofuran-soluble fraction belongs to the
polyester resin in the toner, but not to the polyester resin as a
raw material employed in the production of the toner. That is, for
the case when the properties of the resin to be exerted on the
fixation properties are defined, the properties of the binder resin
in the toner are important.
[0077] The acid value (mg of KOH required to neutralize 1 g of a
resin) of the polyester resin is preferably within a range of 1-30
KOHmg/g because (1) the above molecular weight distribution is
easily obtained, (2) the formation properties of the toner
particles by means of the emulsification/dispersion method are
easily guaranteed, and (3) good environmental stability (stability
of charge properties when the temperature and humidity change) of
the resulting toner is easily retained. The acid value of the
polyester resin can be adjusted by controlling a carboxyl group at
a terminal of the polyester resin by means of the blend ratio and
reaction rate of the polybasic acid and polyhydric alcohol as the
raw materials, in addition to the addition of the monocarboxylic
acid and/or the monoalcohol to the polyester resin obtained by the
polycondensation between the polyhydric carboxylic acid and the
polyhydric alcohol, as described above. Alternatively, a polyester
having a carboxyl group in the principal chain can be obtained by
employing trimellitic anhydride as the polybasic acid
component.
[0078] The toner for electrostatic image development of the present
invention preferably contains a releasing agent. For this case,
waxes selected from the group consisting of hydrocarbon waxes such
as polypropylene wax, polyethylene wax, and Fischer-Tropsch wax;
synthetic ester waxes; and natural ester waxes such as carnauba wax
and rice wax are employed. Among these waxes, natural waxes such as
carnauba wax and rice wax, and synthetic ester waxes such as WEP-5
(produced by NOF Corporation) obtained from a polyhydric alcohol
and a long-chain monocarboxylic acid are preferred.
[0079] The melting point of the wax is not specifically limited,
but is preferably 150.degree. C. or lower in view of the
anti-offset properties. In view of the fixation properties and
storage stability, the melting point is preferably within a range
of 50-120.degree. C. The solid wax may be used as it is, or the wax
may be used in the state of an emulsion. The wax is preferably
dispersed in the toner and is preferably dispersed with an average
particle diameter of 3 .mu.m or less, and more preferably 1 .mu.m
or less. The amount of the wax is preferably within a range of
1-40% by weight based on the toner. When the amount is less than 1%
by weight, the releasability is liable to be insufficient. On the
other hand, when the amount exceeds 40% by weight, the wax is
liable to be exposed on the surface of the toner particles, thereby
lowering the charge properties and storage stability.
[0080] The toner of the present invention preferably contains a
positive charge control agent. The positive charge control agent is
not specifically limited, and known positive charge control agents,
which have conventionally been employed for toner, such as
nigrosine dye, quaternary ammonium compound, onium compound,
triphenylmethane compound and the like may be employed. A compound
having a basic group, such as an amino group, imino group, N-hetero
ring or the like, for example, a tertiary amino group-containing
styrene-acrylic resin, also serves as a positive charge control
agent, and can be used alone or in combination with the above other
positive charge control agent. Depending on the purpose, a small
amount of a negative charge control agent, such as an azo dye metal
complex, salicylic acid derivative metal complex or the like, can
be used in combination with these positive charge control
agents.
[0081] The amount of the positive charge control agent in the toner
of the present invention is preferably within a range of about
0.01-10% by weight, and particularly preferably within a range of
about 0.1-6% by weight. In a production method in which a toner is
produced which contains the positive charge control agent, a
portion of which is exposed on the toner surface, the amount
described above is required. In case the positive charge control
agent is fixed on the surface of the toner particles by various
means, the amount of the positive charge control agent to be added
to the toner surface can be reduced. In this case, the amount is
preferably within a range of 0.01-1%, and particularly preferably
within a range of 0.01-0.5%. It is more preferable to fix the
positive charge control agent on the surface of the toner particles
because the desired proper charging is obtained by employing a
small amount of the positive charge control agent.
[0082] The colorant employed in the toner for electrostatic image
development of the present invention is not specifically limited,
and conventionally known colorants can be employed. A pigment is
preferably employed.
[0083] Examples of black pigment include Carbon Black, Cyanine
Black, Aniline Black, Ferrite, Magnetite, and the like.
Alternatively, black pigments prepared from the following color
pigments can be used.
[0084] Examples of yellow pigment include Chrome Yellow, Zinc
Yellow, Cadmium Yellow, Yellow Iron Oxide, ocher, Titanium Yellow,
Naphthol Yellow S, Hansa Yellow 10G, Hansa Yellow 5G, Hansa Yellow
G, Hansa Yellow GR, Hansa Yellow A, Hansa Yellow RN, Hansa Yellow
R, Pigment Yellow L, Benzidine Yellow, Benzidine Yellow G,
Benzidine Yellow GR, Permanent Yellow NCG, Vulcan Fast Yellow 5G,
Vulcan Fast Yellow R, Quinoline Yellow Lake, Anthragen Yellow 6GL,
Permanent Yellow FGL, Permanent Yellow H10G, Permanent Yellow HR,
Anthrapyrimidine Yellow, Isoindolinone Yellow, Cromophthal Yellow,
Nobopalm Yellow H2G, Condensed Azo Yellow, Nickel Azo Yellow,
Copper Azomethin Yellow, and the like.
[0085] Examples of red pigment include Chrome Orange, Molybdenum
Orange, Permanent Orange GTR, Pyrazolone Orange, Valcan Orange,
Indathrene Brilliant Orange RK, Indathrene Brillant Orange G,
Benzidine Orange G, Permanent Red 4R, Permanent Red BL, Permanent
Red F5RK, Lithol Red, Pyrazolone Red, Watchung Red, Lake Red C,
Lake Red D, Brilliant Carmine 6B, Brilliant Carmine 3B, Rhodamine
Lake B, Arisaline Lake, Permanent Carmine FBB, Perinone Orange,
Isoindolinone Orange, Anthanthrone Orange, Pyranthrone Orange,
Quinacridone Red, Quinacridone Magenta, Quinacridone Scarlet,
Perylene Red, and the like.
[0086] Examples of blue pigment include Cobalt Blue, Cerulean Blue,
Alkaline Blue Lake, Peacock Blue Lake, Phanatone Blue 6G, Victoria
Blue Lake, Metal-free Phthalocyanine Blue, Copper Phthalocyanine
Blue, Fast Sky Blue, Indanthrene Blue RS, Indanthrene Blue BC,
Indigo, and the like.
[0087] The amount of the colorant is preferably within a range of
1-50 parts by weight, and particularly preferably within a range of
3-15 parts by weight, based on 100 parts by weight of the binder
resin.
[0088] To retain good friction charge properties even when the
particle diameter of the toner is reduced, it is effective to
prevent the colorant from being exposed on the surface of the toner
particles, that is, to attain a toner structure wherein the
colorant is included in the toner particles. The impairment of the
charge properties accompanying the reduction in particle diameter
of the toner is also caused by the fact that the colorant and other
additives (e.g. wax, etc.) are partially exposed on the surface of
the toner particles. Even if the content (% by weight) of the
colorant is the same, the surface area of the toner particles is
increased by the reduction in particle diameter and the proportion
of the colorant, wax or the like to be exposed on the surface of
the toner particles is increased. As a result, the composition of
the surface of the toner particles drastically changes and the
friction charge properties of the toner particles drastically
change, thereby making it difficult to obtain proper charge
properties.
[0089] According to the toner of the present invention and method
of producing the same, since the colorant and wax are included in
the binder resin, the charge properties are made uniform, thereby
making it possible to easily obtain a good printed image. It can be
easily determined, for example, by observing the cross section of
the particles employing a TEM (transmission electron microscope)
that the colorant and wax are not exposed on the surface of the
toner particles. More concretely, when the cross section, which was
obtained by embedding the toner particles into a resin and cutting
the resulting sample by a microtome, is optionally dyed with
ruthenium tetraoxide and observed by a TEM, it can be confirmed
that the pigment and wax are included in the binder resin and
dispersed in the particles almost uniformly.
[0090] The toner for electrostatic image development of the present
invention can be produced by a method of mixing a mixture
comprising at least a binder resin made of a polyester resin having
a carboxyl group, a colorant, and a releasing agent with an aqueous
medium, emulsifying and dispersing the admixture in the presence of
a base to form colored particles (I) including at least the
colorant and binder resin therein, separating the colored particles
(I) from the liquid medium, and drying the colored particles.
[0091] The mixture made of the binder resin, colorant, and wax can
be prepared by a conventionally known method and is preferably
prepared by the method of mixing these raw powders and sufficiently
kneading, employing any of a twin-screw extruder, a kneader, and a
twin roll. Since a breakage of the high-molecular weight component
of the binder resin occurs sometimes in such a melt-kneading step,
it is preferable to select the raw resin after previously
confirming a change in the molecular weight during the kneading of
the binder resin to produce a toner comprising the binder resin
having a specific range of flow tester values similar to the toner
of the present invention.
[0092] A method of emulsifying the kneaded mixture in the aqueous
medium by applying high-speed stirring conditions in the presence
of a base can be employed as a method of mixing the kneaded mixture
thus prepared with the aqueous medium and emulsifying the
admixture, for example. Particularly, when employing this process,
it is preferably performed under conditions of high temperature and
high pressure where the binder resin is softened, thereby making it
possible to inhibit the aqueous medium from boiling.
[0093] The toner for electrostatic image development of the present
invention can also be produced by a method of mixing a binder
resin, a colorant, and a releasing agent with an organic solvent,
and kneading and dispersing the mixture employing a wet process to
obtain the above mixture. In this case, the colorant and releasing
agent may be kneaded and dispersed, separately, employing the wet
process.
[0094] Concretely, this is a method of dissolving the binder resin
in the organic solvent, adding the colorant and releasing agent,
dispersing them employing a general mixing/dispersing apparatus
such as a despa (dispersion stirrer), ball mill, beads mill, sand
mill, continuous beads mill or the like, to prepare a resin
solution wherein the colorant and releasing agent are finely
dispersed in the organic solvent, mixing the resin solution with an
aqueous medium in the presence of a basic neutralizer, thereby
emulsifying them, and removing the organic solvent under reduced
pressure to prepare the aqueous medium (suspension) of the colored
particles (I) described above. Then, the colored particles (I) are
separated from the aqueous medium and dried to obtain a toner. This
method is better than the above method wherein high shear is
applied to the resin, because the polymer component (gel component)
is not broken.
[0095] The polyester resin employed to produce the toner for
electrostatic image development of the present invention is a
polyester resin having a carboxyl group.
[0096] The polyester resin having a carboxyl group as an acidic
group becomes self-water dispersible. With respect to the resin
with self-water dispersibility the hydrophilicity increases by
converting the acidic group into an anion, whereby the polyester
resin is dispersed in the aqueous medium (water or a liquid medium
containing water as a principal component).
[0097] Examples of the base employed to neutralize the acidic group
(carboxyl group) include, but are not limited to, inorganic bases
such as sodium hydroxide, potassium hydroxide, and ammonia; and
organic bases such as diethylamine, triethylamine, and
isopropylamine.
[0098] Examples of the organic solvent employed to dissolve or
disperse the binder resin, colorant, and wax (releasing agent)
include hydrocarbons such as pentane, hexane, heptane, benzene,
toluene, xylene, cyclohexane, and petroleum ether; halogenated
hydrocarbons such as methylene chloride, chloroform,
dichloroethane, dichloroethylene, trichloroethane,
trichloroethylene, and carbon tetrachloride; ketones such as
acetone, methyl ethyl ketone, and methyl isobutyl ketone; and
esters such as ethyl acetate and butyl acetate. These solvents can
be employed alone, or two or more kinds of them can be employed in
combination. The organic solvent dissolves the binder resin and is
preferably a solvent having comparatively low toxicity and a low
boiling point, and which is easily removed in the subsequent
processes. Among these organic solvents, methyl ethyl ketone is
most preferable.
[0099] The method of neutralizing the acidic group (carboxyl group)
of the polyester resin with the base includes, for example, (1) a
method of preparing a mixture containing a colorant, a wax, and an
organic solvent employing a binder resin having a previously
neutralized acidic group, or (2) a method of preparing a mixture
containing a binder resin having an acidic group, a colorant, a
wax, and an organic solvent, and neutralizing the mixture with a
base.
[0100] The method of neutralizing the acidic group of the polyester
resin with a base and emulsifying the polyester resin includes, for
example, (3) a method of emulsifying by adding the mixture to an
aqueous medium, or (4) a method of adding an aqueous medium to the
mixture. A combination of methods (2) and (4) is preferred because
the particle size distribution is improved.
[0101] A method of mixing a basic neutralizer in the aqueous medium
may also be employed, but a neutralization/emulsification method
employing the above combination is preferred in view of the
particle size distribution.
[0102] In the method of the present invention, a phase inversion
agent is preferably added to a mixture containing at least a binder
resin made of a polyester resin having a carboxyl group, a
colorant, and a releasing agent, and mixed with an aqueous medium
in the presence of a base. As used herein, the term "phase
inversion agent" differs in function from the emulsifier and
dispersion stabilizer described previously in the "Prior Art"
section. That is, the emulsifier and dispersion stabilizer
described previously in the "Prior Art" section refer to those
which are adsorbed on the surface of the particles and capable of
stably dispersing the particles in the aqueous medium without
causing fusing and agglomeration of the formed particles.
[0103] On the other hand, the phase inversion agents employed in
the method of the present invention refer to agents having a phase
inversion acceleration function. That is, in the step of adding an
aqueous medium (water or a liquid medium containing water as a main
component) to a mixture composed of a binder resin, a colorant or
the like, and an organic solvent, gradual addition of water to the
continuous organic phase of the above mixture produces
discontinuous water-in-oil phases. Further addition of water causes
inversion of the discontinuous water-in-oil phases to discontinuous
oil-in-water phases and forms a suspension in which the above
mixture is suspended as particles (droplets) in the aqueous medium.
At this time, agents having a function of smoothly promoting the
inversion of the water-in-oil discontinuous phase to the
oil-in-water discontinuous phase are referred to as phase inversion
agents.
[0104] As described above, according to the method of the present
invention, particles made of a self-water dispersible resin
obtained by neutralizing the resin can be formed by phase
inversion. Since said particles can stably exist in the aqueous
medium because neutralized functional groups in the resin exist on
the surface of the particles, so-called emulsifier and dispersion
stabilizers are not required.
[0105] The binder resin employed in the present invention can be
dispersed in the aqueous medium without employing the phase
inversion agent because the binder resin is provided with
self-water dispersibility by neutralization. However, a powdered
toner having the preferable average particle diameter and particle
size distribution can be easily produced by employing the phase
inversion agent in the binder resin made of the polyester resin
which satisfies the requirements of the toner of the present
invention. For example, when water is added dropwise while stirring
at low shear employing methyl ethyl ketone as the solvent, the
following phenomenon occurs. That is, when dispersing in water,
microparticles having a particle diameter of about 1 .mu.m are
formed. Alternatively, when a trial of increasing the particle
diameter is made, the viscosity increases during the phase
inversion process, thus causing no phase inversion. When the
dispersion and association are conducted at high shear employing a
homomixer in accordance with the technique disclosed in Japanese
Unexamined Patent Application, First Publication No. Hei 10-319639,
spherical powdered toners having an average particle diameter
suited for use as the toner can be obtained, but microparticles and
coarse particles are formed as described in the "Prior Art"
section, which is not preferred.
[0106] When the phase inversion agent employed in the method of the
present invention is added and a resin capable of meeting the
object of the present invention is employed and, moreover, stirring
is conducted at low shear, it becomes possible to produce a
spherical powdered toner which has an average particle diameter
suited for use as the toner and a sharp particle size distribution,
and which also forms a small amount of microparticles, resulting in
less classification loss.
[0107] The following can be employed as the phase inversion agent
in the present invention.
[0108] (i) alcohol solvent
[0109] (ii) metal salt compound
[0110] Methanol, ethanol, isopropanol, n-propanol, isobutanol,
n-butanol, t-butanol, sec-butanol, ethylene glycol monomethyl
ether, propylene glycol monomethyl ether, ethylene glycol
monomethyl ether, or the like can be employed as the alcohol
solvent, for example. As a matter of course, other alcohol solvents
can also be employed. Isopropanol and n-propanol, which dissolve in
water and have a low boiling point are preferred. The amount of the
alcohol solvent is within a range of about 10-50 parts by weight
based on 100 parts by weight of the solid content of the resin, but
is not limited thereto.
[0111] Conventionally known metal salt compounds can be employed as
the metal salt compound, and salts with metals having two or more
valences are preferred. Examples thereof include barium chloride,
calcium chloride, cuprous chloride, cupric chloride, ferrous
chloride, ferric chloride, and the like. The amount of the metal
salt compound is within a range of about 0.01-3 parts by weight
based on 100 parts by weight of the solid content of the resin, but
is not limited thereto.
[0112] The method of emulsifying/dispersing the mixture of the
binder resin, the colorant, the organic solvent, and the phase
inversion agent in the aqueous medium is not limited to any special
method.
[0113] In the method of the present invention, high shear
emulsification/dispersion apparatuses and continuous
emulsification/dispersion apparatuses can be employed, such as a
Homomixer (produced by Tokushu Kika Kogyo Co., Ltd.), a Slasher
(produced by Mitsui Mining Co., Ltd.), a Cavitron (produced by
Eurotec, Ltd.), a Microfluidizer (produced by Mizuho Kogyo Co.,
Ltd.), a Munton-Golin Homogenizer (produced by Golin Co.), a
Nanomizer (produced by Nanomizer Co., Ltd.), a Static Mixer
(produced by Noritake Company), and the like.
[0114] However, a method of adding water dropwise while stirring at
low shear employing a stirrer, an anchor blade, a turbine blade, a
faudler blade, a full-zone blade, a max blend blade, a semicircular
blade, or the like at a peripheral speed within a range of 0.2-5
m/second, and preferably within a range of 0.5-4 m/second, is
preferred as disclosed in Japanese Unexamined Patent Application,
First Publication No. Hei 9-114135.
[0115] By performing emulsification/dispersion at low shear, the
formation of fine powders can be inhibited and a more preferred
particle size distribution can be realized. Also poor balance of
the molecular weight distribution of the toner particles and poor
fixation properties at low temperatures of the toner are not caused
by the formation of fine powders containing exclusively the
low-molecular weight component of the polyester resin.
[0116] The toner for electrostatic image development of the present
invention can be converted into a positive-charge toner by
employing a positive charge control agent. An example of a method
of producing the positive-charge toner is a method in which a
mixture containing, as essential components, a polyester resin, a
colorant, and a positive charge control agent is mixed and
emulsified with an aqueous medium in the presence of a basic
neutralizer to produce particles, which are separated from the
liquid medium and dried.
[0117] Alternatively, the positive-charge toner can be produced by
preparing a suspension of microparticles (II), which is obtained by
emulsifying a mixture of a positive charge control agent and a
resin capable of being provided with self-water dispersibility
and/or water solubility by neutralization with an aqueous medium in
the presence of a neutralizer containing the positive charge
control agent, mixing the suspension of the microparticles (II)
with a suspension of the colored particles (I) prepared by another
step, adding a compound having a reverse polarity as compared with
the neutralizer, thereby forming the microparticles (III), wherein
the microparticles (II) are deposited on the surface of the colored
microparticles (I), separating the microparticles (III) from the
aqueous medium, and drying the microparticles (III).
[0118] The resin, which is employed in the step of mixing a mixture
containing, as essential components, a resin capable of being
provided with self-water dispersibility and/or water solubility by
neutralization and a positive charge control agent with an aqueous
medium in the presence of a neutralizer and emulsifying the
admixture to obtain a suspension of microparticles (II) containing
the positive charge control agent, is not specifically limited as
long as it is a resin having an acidic group or a basic group.
[0119] Examples of the functional group, which can be converted
into a hydrophilic group by neutralization, include acidic groups
such as a carboxyl group, a phosphoric group, a sulfonic group, a
sulfuric group, and the like. Among these acidic groups, a carboxyl
group is preferable. Examples of the basic group include primary,
secondary and tertiary amino groups, a quaternary ammonium group,
and the like. Among these basic groups, a tertiary amino group is
preferable. Examples of the resin having these functional groups
include a styrene resin, a (meth)acrylic resin, a polyester resin,
a polyurethane resin, an epoxy resin, and the like, and a carboxyl
group-containing styrene-(meth)acrylic resin or polyester resin is
particularly preferably employed.
[0120] Examples of the neutralizer of the acidic group include, but
are not limited to, inorganic bases such as sodium hydroxide,
potassium hydroxide, lithium hydroxide, calcium hydroxide, sodium
carbonate, and ammonia; and organic bases such as diethylamine,
triethylamine, and isopropylamine. Examples of the basic
neutralizer as a compound having a reverse polarity as compared
with the acidic neutralizer include inorganic acids such as
hydrochloric acid, sulfuric acid, and phosphoric acid; and organic
acids such as oxalic acid, formic acid, acetic acid, succinic acid,
and p-toluenesulfonic acid.
[0121] In this case, the average particle diameter of the
microparticles (II) containing the positive charge control agent is
preferably smaller than the particle diameter of the colored
particles (I).
[0122] The average particle diameter of the microparticles (II) is
preferably within a range of about 0.1-1 .mu.m. The content of the
charge control agent in the microparticles (II) is preferably
within a range of about 2-50% by weight, and more preferably within
a range of 3-20% by weight.
[0123] The amount of the microparticles (II), to be added to the
colored particles (I) in the step of adding the suspension of the
microparticles (II) to the suspension of the colored particles (I),
uniformly mixing them, and depositing the microparticles (II) on
the surface of the colored particles (I), is preferably within a
range of about 0.1-10% by weight, and particularly preferably
within a range of 0.5-5% by weight. The deposition of the
microparticles (II) comprising a carboxyl group-containing resin
and a positive charge control agent on the surface of the colored
particles (I) is preferably conducted by adding an aqueous acid
solution having a reverse polarity as compared with that in the
production process of the microparticles (II) to the mixed
suspension of the colored particles (I) and microparticles (II)
while stirring. In this case, the deposition with acid and
salting-out are preferably employed in combination by adding a
small amount of an inorganic salt such as calcium chloride to
attain uniform deposition.
[0124] The colored particles, wherein the positive charge control
agent is fixed on the surface, obtained in the above steps are
fixed more firmly by mixing with stirring while heating (within a
range of 40-80.degree. C. depending on Tg of the resin), employing
a stirrer such as a Henschel mixer after drying.
[0125] With respect to the dispersion of the spherical or generally
spherical colored resin particles obtained by emulsification, it is
preferred that the organic solvent is removed first. Then,
solid-liquid separation of the aqueous dispersion is performed by
means such as filtration and the particles are dried, thus making
it possible to obtain the toner particles. It is preferred that the
colored resin particles obtained by employing the emulsifier or
dispersion stabilizer are washed more adequately.
[0126] With respect to the dispersion of the spherical or generally
spherical colored resin particles obtained by emulsification, it is
preferred that the organic solvent is removed and the
hydrophilicity of the particles themselves is decreased by a
reverse neutralization treatment, wherein acidic and hydrophilic
groups neutralized with an acid such as hydrochloric acid, sulfuric
acid, phosphoric acid, acetic acid or oxalic acid on the surface of
the particles are returned to an original functional group, is
preferably conducted, followed by removal of water and further
filtration and drying.
[0127] The drying can be conducted by employing any of
conventionally known methods, and may be conducted at a temperature
where the toner particles are not thermally fused or agglomerated
under normal or reduced pressure. The freeze-drying method can be
employed. There is also a method of simultaneously separating and
drying the toner particles from the aqueous medium by employing a
spray drier. A method of stirring and drying the powder under
reduced pressure while heating at a temperature where the toner
particles are not thermally fused or agglomerated and a method
employing a flush-jet dryer (produced by Seisin Kigyo Co., Ltd.)
capable of instantaneously drying by use of a heat-dry air flow are
efficient and preferable.
[0128] For the case when the classification for removing coarse
particles and microparticles to adjust the particle size
distribution of the formed toner particles is required, a
conventionally known method employing a commercially available
general air-flow type classifying machine for toner can be
conducted. In a state when the toner particles are dispersed in the
liquid medium, a water slurry of the toner particles may be
classified by utilizing a difference in sedimentation properties
depending on the particle diameter. The removal of the coarse
particles can also be conducted by filtering the water slurry of
the toner particles by employing a filter or a wet vibration sieve.
With respect to the particle size distribution of the toner, a
ratio of 50% particle volume diameter to 50% number particle
diameter as measured by Coulter Multisizer is preferably 1.35 or
less, and preferably 1.25 or less, because a good image is easily
obtained.
[0129] The volume-average particle diameter of the spherical
powdered toner for electrostatic image development of the present
invention is preferably within a range of 1-13 .mu.m in view of the
resulting image quality, and is more preferably within a range of
about 3-10 .mu.m because good matching with a currently existing
machine is easily obtained. In case of a color toner, the
volume-average particle diameter is preferably within a range of
about 3-8 um. When the volume-average particle diameter becomes
smaller, not only are the definition and gradation improved, but
also, the thickness of the toner layer for forming the printed
image becomes smaller, thereby producing the effect of reducing the
amount of the toner to be consumed per page, which is
preferable.
[0130] The powdered toner particles after drying can be employed as
a developing agent as is, but properties such as fluidity and
charge properties are preferably improved by adding an external
additive for toner such as inorganic oxide microparticles, organic
polymer microparticles or the like to the surface of the toner
particles. Examples of the external additive include silica,
titanium oxide, aluminum oxide, vinyl (co)polymer, and the like.
These external additives are preferably added in an amount within a
range of about 0.05-5% by weight based on the weight of the toner
particles.
[0131] The toner of the present invention can be employed for
development of an electrostatic latent image by means of the
electrophotographic method, or employed as a one-component
developing agent or a two-component developing agent mixed with a
carrier. The carrier is not specifically limited, and
conventionally known carriers such as iron powder, ferrite or
magnetite, or carriers coated with a resin can be used.
[0132] The toner of the present invention can be preferably
employed in a printer of a so-called toner-jet system employing
method of directly spraying a powdered toner, which is frictionally
charged by employing a non-magnetic one component developing
apparatus comprising a developing agent bearing roller and a layer
control member, over a paper on a back surface electrode through a
hole on a flexible printed board with an electrode having a
function of controlling the amount of the toner to be passed in the
vicinity, thereby forming an image. Since the toner of the present
invention is superior in fixation properties and color properties
and has a spherical shape, it becomes easy to control scattering of
the toner in a toner-jet system in comparison with a toner having
an unfixed shape.
EXAMPLES
[0133] The following Examples further illustrate the present
invention in detail, but the present invention is not limited
thereto. In the following Examples and Comparative Examples, parts
are by weight and water signifies deionized water.
[0134] (Synthesis Example of Polyester Resin)
[0135] Employing trimellitic anhydride (TMA) as the polyhydric
carboxylic acid, terephthalic acid (TPA) and isophthalic acid (IPA)
as the dihydric carboxylic acid,
polyoxypropylene(2.4)-2,2-bis(4-hydroxyphenyl)propane (BPA-PO) and
polyoxyethylene (2.4)-2,2-bis(4-hydroxyphenyl)propane (BPA-EO) as
the aromatic diol, and ethylene glycol (EG) as the aliphatic diol
in each molar ratio shown in Table 1, tetrabutyl titanate as the
polymerization catalyst was charged in a separable flask in the
amount of 0.3% by weight based on the total amount of monomers. The
flask was equipped with a thermometer, a stirrer, a condenser, and
a nitrogen introducing tube at the upper portion and the mixture
was reacted in an electrically heated mantle heater at 220.degree.
C. for 15 hours in a nitrogen gas flow at normal pressure and,
after gradually evacuating, the reaction was continued at 10 mmHg.
The reaction was monitored by measuring the softening point in
accordance with the ASTM.multidot.E28-517 standard, and the
reaction was completed by terminating the evacuation when the
softening point reached a predetermined temperature.
[0136] The composition and values of the physical properties
(values of properties) of the resin thus synthesized are shown in
Table 1 and Table 2. Table 1 is for a straight-chain polyester
resin, while Table 2 is for a crosslinked polyester resin.
1 TABLE 1 Resin No. R1 R2 R3 Composition TPA 36.9 46.1 36.5 of
Resin IPA 9.2 9.1 TMA BPA-PO 22.5 22.3 BPA-EO 11.3 33.8 11.1 EG
20.1 20.1 21.0 100 100 100 mol/% mol/% mol/% Properties gel
fraction (% 0 0 0 of Resin by weight) T1/2 temperature 100 96 96
(10 kg load) T1/2 temperature 93 90 90 (30 kg load) acid value (KOH
6.7 6.5 3.7 mg/g) Tg (.degree. C.) 54 55 55 Mw (THF-soluble 5700
5600 5500 fraction) Mn (THF-soluble 2100 2600 2700 fraction)
[0137]
2 TABLE 2 Resin No. R4 R5 R6 Composition TPA 31.2 31.2 32.8 of
Resin IPA 11.6 11.6 12.2 TMA 5.2 5.2 3.0 BPA-PO 18.0 22.0 BPA-EO
24.0 6.0 EG 28.0 28.0 30.0 100 100 100 mol/% mol/% mol/% Properties
gel fraction (% 6 12 3 of Resin by weight) T1/2 temperature 163 168
153 (10 kg load) T1/2 temperature 151 152 141 (30 kg load) acid
value (KOH 10.0 8.0 8.5 mg/g) Tg (.degree. C.) 65 64 64 Mw
(THF-soluble 83000 110000 75400 fraction) Mn (THF-soluble 3200 3600
3100 fraction)
[0138] In Table 1 and Table 2, the "T1/2 temperature" is a value
measured at a nozzle diameter of 1.0 mm .PHI..times.1.0 mm, a load
of 10 kg per unit area (cm.sup.2) and a heating speed of 6.degree.
C. per minute employing a Flow Tester "CFT-500" produced by
Shimadzu Corporation. The glass transition temperature Tg is a
value measured at a heating speed of 10.degree. C. per minute by
the second-run method employing a Differential Scanning Calorimeter
"DSC-50" produced by Shimadzu Corporation.
[0139] The T1/2 temperature value, measured by the flow tester
under the same conditions as described above, except that a load of
30 kg was employed, was also described.
[0140] (Preparation Example of Releasing Agent and Releasing Agent
Dispersion)
[0141] 105 parts of a releasing agent, 45 parts of a polyester
resin (R1 in Table 1), and 280 parts of methyl ethyl ketone were
charged in a ball mill and, after stirring for 18 hours, the
mixture was removed and the solid content was adjusted to 20% by
weight to obtain releasing agent microdispersions (W1-W4).
Properties of the resulting releasing agent dispersions are shown
in Table 3.
3 TABLE 3 Releasing Agent Dispersion W1 W2 W3 W4 Releasing Agent PP
PE FT-100 synthetic ester Polyester resin R1 R1 R1 R1 Weight Ratio
of Releasing 70/30 70/30 70/30 70/30 Agent to Resin Endothermic
Peak 140.1 130.2 91.1 84.1 Temperature of Releasing Agent (.degree.
C.) Solid content (% by weight) 20 20 20 20
[0142] The releasing agents shown in Table 3 are as follows.
[0143] PP: "Viscol 660P" (polypropylene wax produced by Sanyo
Chemicals).
[0144] PE: "LICOWAX PE-130PDR" (polyethylene wax produced by
Clariant).
[0145] ET-100: "LUVAX-1211" (Fischer-Tropsch wax produced by Nippon
Seiro Co., Ltd.)
[0146] Synthetic ester: "WEP-5" (synthetic ester wax produced by
NOF Corporation)
[0147] (Preparation Example of Colorant Dispersion)
[0148] A colorant, a resin, and methyl ethyl ketone were charged in
a ball mill so that the solid content became 35-50%, and, after
stirring for 18-36 hours, the mixture was removed and the solid
content was adjusted to 20% by weight to obtain colorant
dispersions (P1-P4). Properties of the resulting colorant
dispersions are shown in Table 4.
4TABLE 4 Colorant Dispersion P1 P2 P3 P4 Colorant Carbon Cyan
Yellow Magenta Resin R1/R4 = R1/R4 = R1/R4 = R1/R4 = 40/60 40/60
40/60 40/60 Weight Ratio of 50/50 50/50 20/80 50/50 Colorant to
Resin Solid Content during 32 32 35 40 Dispersion (%) Dispersion
Time (hour) 18 18 18 36 Solid Content (%) 20 20 20 20
[0149] The colorants shown in Table 4 are as follows.
[0150] carbon: "ELFTEX-8" (produced by Cabot)
[0151] Cyan: "Fastogen Blue TGR" (produced by Dainippon Ink and
Chemicals, Inc.)
[0152] yellow: "Symuler Fast Yellow 8GR" (produced by Dainippon Ink
and Chemicals, Inc.)
[0153] magenta: "Fastogen Super Magenta R" (produced by Dainippon
Ink and Chemicals, Inc.)
[0154] (Preparation of Wet-kneaded Mill Base)
[0155] The above colorant dispersion, a resin, and methyl ethyl
ketone were mixed employing a despa and the solid content was
adjusted to 55% by weight to obtain mill bases (MB1-MB13). Each
formulation of the mill bases thus prepared is shown in Table
5.
5TABLE 5 Mill Colorant Solid Base Dispersion Polyester Resin (I)
MEK Content MB1 P1: 100 parts R1: 30 parts, 15 parts 55% R5: 45
parts MB2 P1: 100 parts R1: 30 parts, 15 parts 55% R4: 45 parts MB3
P1: 100 parts R2: 30 parts, 15 parts 55% R4: 45 parts MB4 P1: 100
parts R1: 21.5 parts, 15 parts 55% R4: 53.5 parts MB5 P1: 100 parts
R3: 38.5 parts, 15 parts 55% R4: 36.5 parts MB6 P1: 100 parts R2:
55.5 parts, 15 parts 55% R5: 19.5 parts MB7 P2: 40 parts R1: 34.8
parts, 63 parts 55% R4: 52.2 parts MB8 P3: 75 parts R1: 32 parts,
35 parts 55% R4: 48 parts MB9 P4: 50 parts R1: 34 parts, 55 parts
55% R4: 51 parts MB10 P1: 100 parts R1: 30 parts, 15 parts 55% R6:
45 parts MB11 P1: 100 parts R1: 55.5 parts, 15 parts 55% 6R: 19.5
parts MB12 P1: 100 parts R1: 75 parts 15 parts 55% MB13 P1: 100
parts R4: 75 parts 15 parts 55%
[0156] (Preparation of Melt-kneaded Mill Base)
[0157] A resin, a colorant, and a releasing agent were premixed and
kneaded in a twin-screw kneader, and then the kneaded mixture was
dissolved and dispersed in methyl ethyl ketone employing a despa
and the solid content was adjusted to 55% to form mill bases. A
color pigment was kneaded by a twin roll to make a master batch.
Each formulation of the mill bases thus prepared is shown in Table
6.
6TABLE 6 Mill Releasing Polyester Solid Base Colorant Agent Resin
(I) MEK Content MB14 carbon carnauba R1: 59.5 parts 200 parts 55%
10 parts 5 parts R6: 25.5 parts MB15 carbon carnauba R1: 34 parts
200 parts 55% 10 parts 5 parts R4: 51 parts MB16 cyan/R1 carnauba
R1: 32.4 parts 200 parts 55% 4 parts/ 5 parts R4: 54.6 parts 4
parts
[0158] The releasing agents and colorants shown in Table 6 are as
follows.
[0159] carnauba: "Carnaubba wax No. 1" (product imported by Kato
Yoko)
[0160] carbon: "ELFTEX-8" (produced by Cabot)
[0161] cyan: "Fastogen Blue TGR" (produced by Dainippon Ink and
Chemicals, Inc.)
Example 1
[0162] 545.5 parts of MB2 shown in Table 5, 115 parts of W4 shown
in Table 3, 57.5 parts of methyl ethyl ketone, 29.0 parts of
isopropyl alcohol as the phase inversion accelerator, and 25.8
parts of an aqueous 1 N ammonia solution were charged in a
cylindrical vessel, followed by sufficient stirring. Subsequently,
230 parts of water were added and the liquid temperature was raised
to 30.degree. C. Then, 44 parts of water were added dropwise while
stirring, thereby performing phase inversion emulsification. The
peripheral speed was 1.05 m/second. After the stirring was
continued for 30 minutes, the rotation was terminated, and 400
parts of water were added.
[0163] A water slurry of particles was observed by an optical
microscope. As a result, agglomerates of the releasing agent were
not observed, and a flowing releasing agent was also not observed.
The particle size distribution was measured by a Coulter Counter.
As a result, Dv/Dn was 1.32, and the occurrence of coarse particles
was not observed.
[0164] The solvent was removed by vacuum distillation, followed by
filtration and washing with water. The resulting wet cake was
dispersed again in water and, after controlling the pH to 4 by
adding an aqueous 1 N hydrochloric acid solution, filtration and
washing with water were repeated. The wet cake thus obtained was
freeze-dried and then classified by an air-flow type classifying
machine to obtain toner particles having a volume-average particle
diameter of 7.4 um and an average roundness of 0.983.
[0165] The resulting toner particles were embedded into a resin and
the resulting sample was cut by a microtome, and then the cross
section dyed with ruthenium tetraoxide was observed by a TEM
(transmission electron microscope). As a result, the pigment and
wax were included in the binder resin and dispersed in the
particles nearly uniformly.
[0166] Employing a Henschel mixer, 1.5 parts of a hydrophobic
silica and 0.5 parts of titanium oxide were externally added to 100
parts of the resulting toner particles to obtain a powdered toner
(for electrostatic image development).
Example 2
[0167] 545.5 parts of MB2 shown in Table 5, 115 parts of W4 shown
in Table 3, 57.5 parts of methyl ethyl ketone, 28.0 parts of
isopropyl alcohol as the phase inversion accelerator, and 26.5
parts of an aqueous 1 N ammonia solution were charged in a
cylindrical vessel, followed by sufficient stirring. Subsequently,
230 parts of water were added and the liquid temperature was raised
to 30.degree. C. Then, 44 parts of water were added dropwise while
stirring, thereby performing phase inversion emulsification. The
peripheral speed was 1.05 m/second. After the stirring was
continued for 30 minutes, the rotation was terminated, and 400
parts of water were added.
[0168] A water slurry of particles was observed by an optical
microscope. As a result, agglomerates of the releasing agent were
not observed, and a flowing releasing agent was also not observed.
The particle size distribution was measured by a Coulter Counter.
As a result, Dv/Dn was 1.35, and the occurrence of coarse particles
was not observed.
[0169] The solvent was removed by vacuum distillation, followed by
filtration and washing with water. The resulting wet cake was
dispersed again in water and, after controlling the pH to 4 by
adding an aqueous 1 N hydrochloric acid solution, filtration and
washing with water were repeated. The wet cake thus obtained was
freeze-dried and then classified by an air-flow type classifying
machine to obtain toner particles having a volume-average particle
diameter of 5.2 .mu.m and an average roundness of 0.981.
[0170] The resulting toner particles were embedded into a resin and
the resulting sample was cut by a microtome, and then the cross
section dyed with ruthenium tetraoxide was observed by a TEM
(transmission electron microscope). As a result, the pigment and
wax were included in the binder resin and dispersed in the
particles nearly uniformly.
[0171] Employing a Henschel mixer, 2 parts of a hydrophobic silica
and 1 part of titanium oxide were externally added to 100 parts of
the resulting toner particles to obtain a powdered toner (for
electrostatic image development).
Comparative Example 1
[0172] 51.0 parts of the resin R4 shown in Table 2, 34.0 parts of
the resin R1 shown in Table 1, 5 parts of a synthetic ester as the
releasing agent, and 10 parts of carbon black "ELFTEX-8" as the
colorant were kneaded in a twin-screw extruder, and the kneaded
mixture was pulverized and then classified to obtain a powdered
toner (Comparative Example 1-1) having a volume-average particle
diameter of 5.4 .mu.m and a powdered toner (Comparative Example
1-2) having a volume-average particle diameter of 7.8 .mu.m,
respectively.
[0173] The resulting powdered toners were observed by a TEM
(transmission electron microscope) in the same manner as those of
Examples 1 and 2. As a result, the pigment and wax were partially
exposed on the surface of the toner particles of Comparative
Example 1-1 and Comparative Example 1-2.
Other Examples and Comparative Examples
[0174] The powdered toners of the other Examples and Comparative
Examples were basically produced in the same manner as in Example
1, and the respective powdered toners were obtained by
appropriately adjusting the amount of solvents such as methyl ethyl
ketone and isopropyl alcohol as the phase inversion accelerator,
the amount of water to be added dropwise, and the amount of the
base.
[0175] The MB (mill base) and releasing agent used, as well as the
measured value of the average roundness of the powdered toners of
the respective Examples and Comparative Examples are shown in Table
7 and Table 8.
7 TABLE 7 Releasing Agent Average Granulation Properties MB Used
Used Dv (.mu.m) Roundness Dv/Dn Example 1 MB2 W4 7.4 0.983 1.32
545.5 parts 115 parts Example 2 MB2 W4 5.2 0.981 1.35 545.5 parts
115 parts Comp. Example 1-1 W4 5.4 0.950 115 parts Comp. Example
1-2 WEP-5 7.8 0.948 Example 3 MB1 WEP-5 7.3 0.978 1.38 545.5 parts
Example 4 MB3 W4 5.3 0.983 1.32 545.5 parts 115 parts Example 5 MB4
W4 7.5 0.977 1.42 545.5 parts 115 parts Example 6 MB5 W3 7.5 0.981
1.44 545.5 parts 115 parts Example 7 MB6 W4 7.3 0.985 1.47 545.5
parts 115 parts Example 8 MB7 W4 7.6 0.978 1.30 545.5 parts 115
parts Example 9 MB8 W4 7.3 0.975 1.33 545.5 parts 115 parts
[0176]
8 TABLE 8 Granulation Releasing Agent Average Properties MB Used
Used Dv (.mu.m) Roundness Dv/Dn Example 10 MB9 W4 7.2 0.976 1.36
545.5 parts 115 parts Example 11 MB10 W4 7.5 0.981 1.36 545.5 parts
115 parts Example 12 MB2 W1 7.6 0.983 1.47 545.5 parts 115 parts
Example 13 MB2 W2 7.4 0.982 1.43 545.5 parts 115 parts Example 14
MB15 carnauba 7.3 0.980 1.34 545.5 parts Example 15 MB16 carnauba
7.5 0.979 1.35 545.5 parts Comp. Example 2 MB11 W4 7.4 0.983 1.45
545.5 parts 115 parts Comp. Example 3 MB12 W4 7.3 0.985 1.53 545.5
parts 115 parts Comp. Example 4 MB13 W4 7.4 0.978 1.51 545.5 parts
115 parts Comp. Example 5 MB14 carnauba 7.6 0.983 1.38 545.5
parts
[0177] The glass transition temperature Tg, the flow beginning
temperature Tfb of the toner as measured by a constant load
extrusion type capillary rheometer, the T1/2 temperature, the flow
ending temperature Tend, the THF-insoluble fraction, and the
fixation temperature range of the powdered toners of the respective
Examples and Comparative Examples were measured, respectively. The
results are shown in Table 9. Furthermore, it was determined
whether the toners of the respective Examples and Comparative
Examples met the relationship: T1/2 (toner).gtoreq.T1/2 (resin).
The results are also shown in Table 9 (in Table 9, this is shown as
T1/2 (toner).gtoreq.T1/2 (resin)).
[0178] The glass transition temperature Tg was measured at a
heating speed of 10.degree. C. per minute by the second-run method
employing a Differential Scanning Calorimeter "DSC-50" produced by
Shimadzu Corporation, in the same manner as in Table 1 and Table 2.
The flow beginning temperature Tfb, the T1/2 temperature, and the
flow ending temperature Tend were measured by employing a Flow
Tester "CFT-500" produced by Shimadzu Corporation, as described in
FIG. 1A and FIG. 1B.
[0179] The measurements were performed under a load of 10 kg and 30
kg.
[0180] With respect to the fixation temperature range, the fixation
temperature was determined by the following fixing properties test,
and the fixation temperature range is indicated by the range
between the upper and lower limits.
[0181] (Fixation Properties Test)
[0182] Employing each of the powdered toners of the Examples and
Comparative Examples, the respective printed papers were fixed by
passing through a heat roller (oilless type) Ricoh Imagio DA-250 at
a speed of 90 mm/second, and then cellophane tape was applied on
the image after fixation. The surface temperature range of the heat
roller when the ID (image density) after peeling was 90% or more of
the original ID and an offset did not occur is defined as the
"fixation temperature".
9 TABLE 9 Fixation Tg 10 kg Load (.degree. C.) 30 kg Load (.degree.
C.) THF-insoluble T{fraction (1/2 )}(T) .gtoreq. Temperature
(.degree. C.) Tfb T1/2 Tend Tfb T1/2 Tend Fraction T{fraction (1/2
)}(R) Range (.degree. C.) Example 1 60.0 117 149.5 158.5 104 136
145 3.8 .largecircle. 115-210 Example 2 59.0 116 149 157.5 103 136
144 3.8 .largecircle. 113-210 Comparative 57.0 110 130 137 101 122
130 0.5 x 123-190 Example 1-1 Comparative 56.5 109 128.5 137 101
121 130 0.5 x 121-193 Example 1-2 Example 3 60.5 118 152 163 106.5
140 150 6.0 .largecircle. 116-220 Example 4 60.0 116 148 158 104
135 145 3.6 .largecircle. 115-210 Example 5 62.0 120 153 162 107
140 149 4.4 .largecircle. 126-220 Example 6 58.0 110 147 158 99 134
145 3.2 .largecircle. 113-200 Example 7 56.0 103 140 150 92 130 140
3.5 .largecircle. 110-192 Example 8 59.0 115 148 158 103 135 145
3.8 .largecircle. 118-205 Example 9 59.5 116 147 159 104 134 146
3.6 .largecircle. 118-205 Example 10 59.5 117 149 159 104 136 146
3.8 .largecircle. 119-205 Example 11 60.0 110 140 148 100 130 138
1.5 .largecircle. 112-200 Example 12 60.5 117 148.5 158 104 136 146
3.8 .largecircle. 125-200 Example 13 59.5 116 149 158.5 103 137 147
3.7 .largecircle. 120-200 Example 14 60.5 107 130 138 99 122 130
0.5 x 119-189 Example 15 60.0 108 130.5 138 100 122.5 130 0.5 x
119-193 Comparative 56.0 105 118 128 98 110 120 0.8 .largecircle.
120-160 Example 2 Comparative 54.0 87 102 107 80 95 100 0
.largecircle. 120-130 Example 3 Comparative 66.0 138 167 180 125
161 171 5.7 .largecircle. 150-220 Example 4 Comparative 55.0 98 118
123 91 111 115 0 x 118-160 Example 5
[0183] It is confirmed from the results shown in Table 9 that the
powdered toner of the Examples of the present invention has a good
fixation initiation temperature and anti-hot offset temperature and
also has a wide fixation temperature range.
[0184] The THF-soluble fractions (GPC measurement results) in the
powdered toners of the respective Examples and Comparative Examples
are shown in Table 10. This GPC measurement was performed in the
same manner as the molecular weight measurement of the binder resin
made of the above polyester resin according to the gel permeation
chromatography (GPC) method.
10 TABLE 10 THF-soluble Fraction in Toner: GPC Measurement Results
Weight-average Molecular Weight Mw/Mn >600000 <10000 Example
1 49700 20.5 1.5 63.0 Example 2 48300 19.8 1.53 62.5 Comparative
56300 18.8 0.85 64.3 Example 1-1 Comparative 56500 18.3 0.85 64.1
Example 1-2 Example 3 52400 23.8 1.75 63.5 Example 4 48700 21.5
1.63 64.8 Example 5 45300 23.1 2.35 55.0 Example 6 45200 18.9 1.23
67.5 Example 7 35600 17.2 0.5 78.5 Example 8 48500 21.5 1.60 63.8
Example 9 49100 22.3 1.55 64.3 Example 10 48800 21.2 1.50 62.9
Example 11 42200 18.9 1.15 65.1 Example 12 48900 21.2 1.60 64.6
Example 13 49300 20.6 1.52 62.8 Example 14 52000 18.1 0.80 65.2
Example 15 54500 17.6 0.75 65.2 Comparative 34600 18.3 0.30 84.5
Example 2 Comparative 5800 2.7 0 100 Example 3 Comparative 88000
25.2 3.5 40.0 Example 4 Comparative 23000 7.5 0.3 84.3 Example
5
[0185] (Image Formation Test)
[0186] With respect to the powdered toners of the respective
Examples and Comparative Examples, the image was formed by
employing a commercially available non-magnetic single-component
system printer, and then the fogging, definition, gradation, OHP
transparency, and transfer efficiency were evaluated,
respectively.
[0187] The results are as shown in Table 11.
11 TABLE 11 OHP Transfer Trans- Efficiency Fogging Definition
Gradation parency % Example 1 .smallcircle. .smallcircle.
.smallcircle. 98 Example 2 .smallcircle. .circleincircle.
.circleincircle. 97 Comp. Example 1-1 x -- -- 87 Comp. standard
standard standard 88 Example 1-2 Example 3 .smallcircle.
.smallcircle. .smallcircle. 97 Example 4 .smallcircle.
.circleincircle. .circleincircle. 98 Example 5 .smallcircle.
.smallcircle. .smallcircle. 97 Example 6 .smallcircle.
.smallcircle. .smallcircle. 98 Example 7 .smallcircle.
.smallcircle. .smallcircle. 98 Example 8 .smallcircle.
.smallcircle. .smallcircle. .smallcircle. 96 Example 9
.smallcircle. .smallcircle. .smallcircle. .smallcircle. 96 Example
10 .smallcircle. .smallcircle. .smallcircle. .smallcircle. 95
Example 11 .smallcircle. .smallcircle. .smallcircle. 97 Example 12
.smallcircle. .smallcircle. .smallcircle. 98 Example 13
.smallcircle. .smallcircle. .smallcircle. 98 Example 14
.smallcircle. .smallcircle. .smallcircle. 98 Example 15
.smallcircle. -- -- .smallcircle. 97 Comp. .smallcircle.
.smallcircle. .smallcircle. 98 Example 2 Comp. -- -- -- -- Example
3 Comp. .smallcircle. .smallcircle. .smallcircle. 97 Example 4
Comp. .smallcircle. .smallcircle. .smallcircle. 98 Example 5
[0188] The fogging, definition, and gradation were visually
evaluated by employing a test pattern. The results were evaluated
by the following criteria.
[0189] .smallcircle.: slightly better than the standard
[0190] .circleincircle.: much better
[0191] The transfer efficiency was represented by a value
determined by the following method of measuring the transfer
efficiency.
[0192] (Method of Measuring the Transfer Efficiency)
[0193] Employing a commercially available printer and copying
machine, a solid image (100 mm long and 20 mm wide) was developed
and the printer and copying machine were stopped when the solid
image on the photosensitive material passed through the
transferring portion by 50%. Then, the image on the photosensitive
material after transferring the non-transferred image (solid) was
completely peeled off by a tape (30 mm.times.20 mm) and the amount
of the toner of the non-transferred image and the amount of the
toner after transferring were measured. The transfer efficiency (%)
is calculated by the following equation.
Transfer efficiency=100-((amount of toner after
transferring)/(amount of toner of non-transferred
image)).times.100
[0194] (Method of Evaluating OHP Sharpness)
[0195] A non-fixed image from a color toner was formed on an OHP
sheet and the non-fixed image was fixed by a separately prepared
fixing tester. The OHP sheet was fixed by passing through a heat
roller (oilless type) Ricoh Imagio DA-250 at a heat roller
temperature of 160.degree. C. and a speed of 90 mm/second. A
black-printed OHP sheet was placed on the OHP sheet made by the
above procedure and was projected on a screen by an overhead
projector, and then the sharpness of letters was visually observed.
The results were evaluated by the following criteria.
[0196] .smallcircle.: sharp letters
[0197] .times.: blurry letters
[0198] It was confirmed from the results shown in Table 11 that the
powdered toners of the Examples of the present invention are
superior in fogging, definition, gradation, and transfer
efficiency. With respect to the OHP transparency, it was confirmed
that the letters are sharp in any of the Examples evaluated.
[0199] With respect to the powdered toners of the Examples, each of
the toners was mixed with a silicone-coated ferrite carrier
(particle diameter of 80 .mu.m) so that the toner concentration
became 3% by weight, and the image was formed by employing a
commercially available non-magnetic single-component system
printer. As a result, a good image was obtained.
[0200] With respect to the toners of the Examples and Comparative
Examples, a heat-resistant blocking test was performed at
50.degree. C. for three days. As a result, no agglomeration was
observed in any of the toners.
Example 16
[0201] (Synthesis Example of Styrene-methacrylic Resin)
[0202] 200 parts of methyl ethyl ketone were charged in a reaction
vessel and heated to 80.degree. C. Then, a mixture of 23 parts of
acrylic acid, 180 parts of styrene, 54 parts of methyl
methacrylate, 43 parts of 2-ethylhexyl acrylate, and 2.2 parts of
"Perbutyl O" (produced by NOF Corporation) was added dropwise for
two hours. After the completion of the dropwise addition, 0.6 parts
of Perbutyl O were added to the reaction solution every four hours,
and the reaction was continued at 80.degree. C. for 24 hours to
obtain a resin. This resin was a non-crosslinked resin having these
physical properties: acid value, 60; Tg, 70.degree. C.; and
weight-average molecular weight, 50,000.
[0203] (Preparation Examples of Microparticles Containing Positive
Charge Control Agent)
[0204] 90 parts of the styrene-methacrylic resin were dissolved in
122 parts of MEK (methyl ethyl ketone) and 111 parts of THF
(tetrahydrofuran) were added, and, furthermore, 102 parts of an
aqueous 1N sodium hydroxide solution, and 10 parts of "BONTORON
N-07" (produced by Orient Chemical) were added, followed by mixing.
2160 parts of water were added in a single portion while stirring,
thereby granulating the microparticles (II) containing a positive
charge control agent. Then, MEK and THF were distilled by vacuum
distillation to obtain a water dispersion (solid content: 5% by
weight) of microparticles (II).
[0205] (Preparation Example of Positive-charge Toner)
[0206] 20 parts of the water dispersion of the microparticles (II)
obtained above and 14.4 parts of an aqueous 1 wt % calcium chloride
solution were added to 500 parts of the water dispersion of colored
particles (I) (solid content: 100 parts) obtained in Example 1
after removing the solvent, followed by sufficient stirring.
Subsequently, the pH was adjusted to 2.5 by adding dropwise an
aqueous 0.1N hydrochloric acid solution while stirring, thereby
depositing the microparticles (II) on the surface of the colored
particles (I). After filtration and washing with water were
repeated, the wet cake was freeze-dried. Employing a Henschel
mixer, the resulting dried powder was mixed with stirring under
heating conditions at 70.degree. C. and then stabilized by
sufficiently fixing the microparticles (II) adhered on the surface.
Then, the resultant was classified by an air-flow type classifying
machine to obtain toner particles having a volume-average particle
diameter of 7.3 .mu.m and an average roundness of 0.982.
[0207] The toner particles were embedded into a resin and the
resulting sample was cut by a microtome, and then the cross section
dyed with ruthenium tetraoxide was observed by a TEM (transmission
electron microscope). As a result, the pigment and wax were
included in the binder resin and dispersed in the particles nearly
uniformly.
[0208] Employing a Henschel mixer, 0.5 parts of silica HVK2150
(Clariant) were externally added to 100 parts of the toner
particles to obtain a positive charge powdered toner.
[0209] (Physical Properties of Positive-charge Toner)
[0210] Tg of the toner was 60.degree. C., Tfb under a load of 10 kg
was 117.degree. C., T1/2 was 149.degree. C., and Tend was
158.degree. C.; Tfb under a load of 30 kg was 104.degree. C., T1/2
was 136.degree. C., and Tend was 145.degree. C.; the THF-insoluble
fraction was 3.6%, and T1/2 (T).gtoreq.T1/2 (R).
[0211] (Image Formation Test of Positive-charge Toner)
[0212] With respect to the developer obtained by mixing 3 parts of
a positive-charge powdered toner with 100 parts of a silicone
resin-coated ferrite carrier (average particle diameter: 80 .mu.m),
the image was formed by employing a commercially available copying
machine (Z-52 produced by Sharp Co.), and then the fogging,
definition, gradation, and image density were evaluated. As a
result, a good image was obtained.
[0213] (Fixation Properties Test of Positive-charge Toner and
Results)
[0214] The non-fixed printed papers obtained by the above copying
machine were fixed by passing through a heat roller (oilless type)
Ricoh Imagio DA-250 at a speed of 90 mm/second, and then cellophane
tape was applied on the image after fixation. The surface
temperature range of the heat roller when the ID (image density)
after peeling was 90% or more of the original ID and an offset did
not occur is defined as the "fixation temperature". As a result,
the fixation temperature was within a range of 116-210.degree.
C.
* * * * *